Video system

ABSTRACT

In a video system for displaying a video picture composed of image points, whose color values and/or brightness values can be stored sequentially, according to a first set of parameters with predetermined parameter values containing number of lines, number of image points, line frequency and frame frequency as parameters, in an image storage which can be read out in accordance with a second set of parameters with different or identical parameter values for the parameters for displaying the stored video picture by means of a display device, the display device contains an individual light source which can be controlled in accordance with the color values and/or brightness values of the image points and whose light bundle can be projected onto a picture screen via an optical system, wherein the optical system has a raster scanning device by which the light bundle can be directed onto the picture screen on optional points within an image field for displaying the video picture of suitable dimensions and for which a raster control is provided for rastering the light bundle in accordance with the second set of parameters.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a video system for displaying a videopicture composed of image points, whose color values and/or brightnessvalues can be stored sequentially, according to a first set ofparameters with predetermined parameter values containing number oflines, number of image points, line frequency and frame frequency asparameters, in an image storage which can be read out in accordance witha second set of parameters with different or identical parameter valuesfor the parameters for displaying the stored video picture by means of adisplay device.

2. Description of the Related Art

Video systems of this type are known, e.g., from DE 29 38 349 A1. Thisreference describes a circuit arrangement for increasing resolution andfor preventing flickering and an image storage with a video picturewhich is read out again at twice the speed.

Another application of image storages is known from DE 41 39 842 A1.This reference describes a video system by which the video picture isprojected by means of lasers. Since the light intensity of the lasers islow, the received video picture is divided into partial areas in animage storage and these partial areas are imaged by means of differentlaser projectors.

Such image storages can also be used, for example, for converting fromone standard to another, the aforementioned parameter sets beingdetermined by the standard of the input signals and output signals.Including the high-resolution systems currently under development, thestandards are substantially as follows: PAL, PAL PLUS, PAL 50-Hz framefrequency, PAL 100-Hz frame frequency, HDTV, HD-MAC, NTSC, and MUSE.

Generally, the possibility of storing video pictures with a givenstandard in an image storage and reading them out of the image storagefor display with a different standard is very limited, since TV systemsmust use a picture tube adapted specifically to a standard and thenumber of lines as well as the aspect ratio of different systemsrelative to one another can change. This limitation becomes especiallyapparent in color television, since images can only be shown with aresolution determined by an aperture mask in the picture tube. This isalso true for LCD projectors in which the density of image points isgiven by the structure of the LCD matrix to be projected.

Therefore, it has so far been impossible to construct a video systemwhich can receive images in different standards and also display them inoptional different standards.

OBJECT AND SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a video systemwhich receives signals of a video picture on the input side inaccordance with a first set of parameters corresponding to a specifiedstandard and displays this image according to a different, second set ofparameters for displaying images which is determined by the same or by adifferent optional standard.

Proceeding from the prior art mentioned above, this object is met inthat the display device contains an individual light source which can becontrolled in accordance with the color values and/or brightness valuesof the image points and whose light bundle can be projected onto apicture screen via an optical system, wherein the optical system has araster scanning device by which the light bundle can be directed ontothe picture screen on optional points within an image field fordisplaying the video picture of suitable dimensions and for which araster control is provided for rastering the light bundle in accordancewith the second set of parameters.

The video system according to the invention differs from the prior artmentioned above in that every optional point on the picture screen canbe illuminated for display by means of the light bundle so that,according to the invention, there is no limitation imposed, for example,by aperture masks or LCD matrices. Further, aperture masks forgenerating different colors can be dispensed with according to theinvention because the rastered light bundle itself is controlled withrespect to color and brightness. In order to generate the light bundle,the light source can be provided with three differently colored lasers,for example, which are controlled by RGB signals from the image storageand whose laser beams are unified by a mirror system to form a commonlight bundle.

Only one light bundle is provided so that there is no need, according tothe invention, to divide the video picture into partial images which aredisplayed independently from one another. This substantially increasesimage quality without additional expenditure on adjusting means, sincepossible overlapping in the display of partial images is preventedthrough the use of an individual light bundle which scans the entireimage field.

When the light bundle proceeding from the light source is very parallel,as is the case in the example given above with lasers, the picturescreen for displaying can also be moved away from the raster scanningdevice as far as desired without a loss of sharpness. Thus, differentimage dimensions can be produced by this technique simply by adjustingthe picture screen distance. This results in considerable flexibilitywith respect to displayable image dimensions and a video system of thiskind can be manufactured for small as well as very large image sizeswithout an increase in technical expenditure.

Acousto-optical beam deflectors can be used, for instance, for thedeflection of the light bundle. However, these deflection devicesusually permit only very small deflection angles which means that thepicture screen must be arranged at a considerable distance from theraster scanning device for correspondingly large images. For thisreason, a preferred further development of the invention in which theraster scanning device has mirrors for deflecting the light bundle ismore advantageous. Mirrors permit a substantially greater deflectionangle so that the distance between the picture screen and the rasterscanning device can be kept smaller than is possible withacousto-optical deflection.

The maximum possible deflection of a mirror is not limited so thatdifferent image sizes can be generated on the picture screen in a simplemanner, that is, variable image sizes are made possible withoutadjusting the picture screen relative to the raster scanning device.

According to a preferred further development of the invention, themirrors are constructed as rotating mirrors and/or swiveling mirrors.

Above all, rotating mirrors which are designed as polygon mirrors inwhich every side of the polygon is constructed as a mirror for scanninga line provide raster scanning with high deflection speed. When thepolygon has a large number of sides, very high line frequencies arepossible, since the line frequency is given by the revolutions perminute divided by the number of polygon sides. Further, due to theirinertia, rotating mirrors ensure a very favorable synchronous runningwhich can only be achieved in other types of deflection, e.g.,acousto-optical deflection, by a commensurate expenditure onelectronics.

For synchronization of lines, image storages are conventionallyoutfitted with their own generator which synchronizes the readout of theindividual brightness values and color values from the image storage.However, in the indicated video system this would require a preciseregulation of the position of the rotating mirror, which would result inincreased expenditure on electronics. Therefore, it is provided in afurther development of the invention that the image storage can be actedupon by synchronizing pulses for the start of the line and/or the startof the frame from the raster control for the readout of the videopicture. In this further development of the invention, the synchronizingpulses can be obtained, e.g., from the actual rotation of the rotatingmirror. In this case, the speed of the rotating mirror need not coincideexactly with the line frequency. Thus, the required technicalexpenditure is reduced as a result of this further development.

The synchronizing pulses can be obtained, e.g., inductively or bydetermining the time at which the light bundle, e.g., of a measurementlaser or the light source itself, is reflected by a polygon surface.

In the case of very high frame frequencies and line frequencies, memorydelays must also be taken into account for synchronization. Such delaysmay vary sharply from one case to another since the signal processingcan differ widely for different numbers of image points and linesdepending upon the input standard and output standard. This can causeproblems with the synchronization of the read-out image. These problemsare solved, according to a further development of the invention, in thatthe synchronizing pulses of the raster control can be generated prior intime to the start of each line which is given by the raster control by atime interval determined by the maximum memory delays and a delaycircuit is provided for adapting the synchronizing signals to the actualdelay time.

Due to this further development, the synchronizing pulses can begenerated at a permanently defined time point with reference to thestart of a line, which does not require any mechanical modifications forthe picking up of synchronizing pulses by the movable mirrors fordifferent operating conditions, e.g., when one of the parameter setschanges. On the other hand, the delay time is adjusted purelyelectronically by means of the delay circuit by a time determined by theparameter set representing the desired image processing in the imagestorage.

Widely different types of storages can be used as image storages, e.g.,analog storages, one of which is provided for each color signal in thecolor video pictures. Such image storages store the images electrically,for instance, via an electron beam as charges on a plate, or opticallyon a persistent screen, wherein the plate or screen can be read outagain as in a television camera by means of a second electron beam. Theadvantage in such image storages consists in that only a smallexpenditure is required for standards conversion. However, signalprocessing is possible only to a very limited degree, since such animage storage does not permit the application of special mathematicalalgorithms for changing the resolution for the second set of parameterswithout a large expenditure for signal conversion.

However, another preferred further development of the invention providesa digital storage in which the quantity of available storage locationsis greater than or equal to the number of required storage locations forstoring the color values and/or brightness values multiplied by themaximum number of displayable image points and the available storagelocations are freely addressable by the color information and/orbrightness information.

A digital image storage permits the use of various algorithms for imageprocessing, above all when it is freely addressable. A video processorcan be used for this purpose, this video processor working with the samestorages and processing the images, e.g., by means of known algorithmsfor increasing or decreasing resolution, depending on whether or not theparameter set for display requires a higher or lower resolution than theparameter set for reading into the storage.

Digital storages are also obtainable at a lower cost and are morereadily available than analog storages which are hardly in use anymore.

The prescription indicated above for selecting the number of storagelocations limits the expenditure on the storage locations to thoseneeded for the number of image points. Accordingly, better use can bemade of the storage locations, e.g., compared with the storage of colorvalues and/or brightness values in accordance with the address withrespect to lines. In this case, the selected quantity of storagelocations would have to be at least as great as the maximum number oflines multiplied by the maximum possible quantity of image pointsoccurring per line, which generally requires a substantially largerstorage area. On the other hand, when the digital storage is selected,the data are stored in the storage sequentially in accordance with thetime sequence for display so that access time is very fast.

Since pulses for reading into and reading out of the image storage canalso occur simultaneously in the indicated video system as a result ofthe different line frequencies of the first parameter set and secondparameter set, problems arise due to the fact that a storage location inthe storage can be addressed either via the address for reading in orthose for reading out, but cannot be addressed simultaneously by both.Therefore, reading in and reading out should be synchronized with oneanother. A simple gate circuit which, e.g., prohibits reading in duringreadout, is not recommended for this purpose as data may be lost.

However, a preferred further development of the invention provides thatthe digital image storage has a priority circuit which, in the event ofsimultaneous addressing for storing in storage locations and for readinginformation out of storage locations, gives priority to the addressingfor readout, temporarily stores the address for storage as well as theinformation to be stored, and only stores this information in thestorage when the readout is concluded.

This circuit reserves priority for readout, which is advisable chieflybecause, in the interest of achieving good image quality, no waitingperiods for displaying an image point are permitted with rotating andswiveling mirrors because of the inertia. In this further development ofthe invention, the image information on the input side is also not lostbecause it is stored temporarily and is read into the image storagelater, given available time at the conclusion of the readout. As will bemade clear in the following with reference to an embodiment example,this can easily be realized by means of suitable electronic controlequipment via a FIFO (first in, first out) storage for temporarystorage.

The quality of the image display is advantageously increased by means ofthis feature without substantial expenditure.

According to another preferred further development of the invention, thequality of the image is increased in that an image processing device, inparticular a video processor, is provided which interpolates the imagepoints, in accordance with the second parameter set for display, fromthe brightness values and/or color values of the stored video picturewhen the number of image points and/or lines in the first parameter setis different than that in the second parameter set.

As a result of the image processing device, color values and brightnessvalues from the first parameter set for displaying the video picture canalso be transformed with the second parameter set. This is advantageousabove all when the number of image points and/or the number of lines isdifferent from that of the read-in image. By way of illustration, itwill be assumed, for example, that the number of lines which areprovided for display is twice that of the lines in the image which isread into the image storage. In this case, every second line in theimage display could be interpolated from the preceding and followinglines of the stored image with reference to the frame. Variousalgorithms are available for interpolating. Flexibility with respect tothe various algorithms is achieved in that a video processor, forexample, is used as an image processing device.

However, when there is a large number of image points, time problems canoccur in currently available video processors, particularly when using acomplex algorithm with many multiplications. This time problem can beavoided, according to a further development of the invention, in that asecond storage or storage area is provided in which brightness valuesand/or color values which are interpolated by the image processingdevice are stored for readout for the display device. Thus, two storageareas are obtained for the image to be read in and read out, whichincreases the available time for the video processor to the time of animage and avoids storage access via auxiliary storage areas for carryingout intermediate calculations. Further, synchronization problems betweendata to be read in and data to be read out can be reduced when thestorage or storage areas used for reading in and reading out areaddressable independently from one another. Synchronization problems fordata access by the video processor can be avoided by means ofcommercially available DMA (direct memory access) modules.

Further, the separation of storage areas for reading in and for readingout is advantageous in that a plurality of image processors to whichdifferent portions of the image are allocated for processing can work inparallel, which further reduces the available time for thetransformation of the brightness values and/or color values for display.

According to a preferred further development of the invention, anotherpossibility for reducing the image processing time consists in that morethan one line can be read into the image processing device from theimage storage, wherein the color values and/or brightness values of thelines which are read in can be subjected to analog summation in aweighted manner for generating a line for display. Based on such ananalog circuit, multiplications are carried out very quickly, enablinghigher rates for the display of an image than would be possible withdigital interpolation by means of a video processor. As will be seenfrom an embodiment example hereinafter, different algorithms can also beused in a weighted summation of this kind. Accordingly, considerableflexibility is possible for different algorithms similar to thatachieved in video processors.

The method of analog summation can be applied not only between lines,but also between image points of a line in that the color values andbrightness values of a line can be summed in analog in a weighted mannerfrom the image storage with respect to time, e.g., via an image pointclock.

Alternatively, in a preferable further development of the invention, alow-pass filter is provided in the image processing device, thislow-pass filter having a cutoff frequency which is given by apredetermined factor multiplied by the smallest product of the imagepoint/line times the line frequency with respect to both sets ofparameters.

According to this further development, the interpolation between colorvalues and brightness values within a line is effected in analog by thelow-pass filter. The parameter determining the interpolation is thecutoff frequency of the low-pass filter. The cutoff frequency issubstantially given by the greater time per image point determined bythe two sets of parameters. If the image point time for the read-inimages is greater than that of the image points for display, the signalfor the image point, which is a square pulse because of the digitalimage storage, must be smoothed via the low-pass filter for displayingthe image point, since otherwise an ambiguity in hue which could resultin flickering of the image results at the sharp flanks of the squarepulses in the higher-resolution display.

On the other hand, if the duration of an image point for display isgreater than that for a stored image point, the color values andbrightness values for the display are not accurately fixed on thepicture screen with respect to the location of the displayed imagepoint. In either case, the greater of the durations per image point ofboth parameter sets is the favorable time constant of the low-passfilter. The factor indicated in this feature determines the degree ofaveraging over successive image points and accordingly fixes theinterpolation between the image points. The factor accordingly allows acertain flexibility in the selection of the interpolation algorithm.

Most of all, this further development of the invention enablesparticularly fast image processing and resolution adaptation of thedisplayed images from the images which are read in. A further advantageconsists in that high-frequency interference which can originate fromthe intermediate frequency, for example, is also filtered out by thelow-pass filter. The displayed images are accordingly substantially freeof interference.

Low-pass filters generally have capacitors which can charge duringsignal processing of the kind mentioned above so that the brightness maychange somewhat from line to line. By including a black-level porch atthe start of the line as information in the image storage, a shift ofthis kind can be compensated for automatically by interpolation.However, it is possible to economize on the additional storage spacerequired for this purpose in that, with every line generated in thisway, the black level is redefined prior to each displayed line by meansof a clamping circuit, as is known from conventional televisiontechnique. Therefore, in a further development of the invention, aclamping circuit is provided downstream of the low-pass filter. Thisfeature improves the display quality and reduces the required storagespace.

The primaries for the color values can differ sharply in the imageswhich are read into the image storage. For instance, the FCC standardfor color definition diverges from that of the EBU standard, above all,for the color green. For this reason, it is advisable for adaptingvarious standards, according to a preferred further development of theinvention, to provide a circuit for color adaptation in the event ofdifferent signal definitions for color values and/or brightness valuesin the parameter sets for storing and readout. In this way, huedistortions due to different standards are also compensated for and thequality of the image display by the video system according to theinvention is improved.

The invention will be explained more fully in the following in principleby way of example with reference to drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a video system according to the invention with laserprojection;

FIG. 2 shows a circuit for an image storage which can be used in a videosystem according to FIG. 1;

FIG. 3 shows an image storage in which signal processing is carried outby means of a video processor; and

FIG. 4 shows a circuit with an image storage in which the color valuesfor the displayed image points are processed in analog fashion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a video system into which color value signals R, G, B andsynchronizing signals are fed in accordance with a first set ofparameters containing number of lines, number of image points, linefrequency, frame frequency, and signal definition for color andbrightness of the image points, This parameter set can be determined bya standard, for example, corresponding to PAL, PAL PLUS, PAL 50-Hz framefrequency, PAL 100-Hz frame frequency, HDTV, HD-MAC, NTSC, or MUSE. Thesynchronizing signals of the video picture are applied to the inputs ofa system control circuit 10. The system control circuit 10 serves togenerate, manage and prepare all control signals used in the videosystem according to FIG. 1 in accordance with separate sets forparameters for reading in and for displaying the video picture. For thestorage of digitally converted RGB signals, it generates the storageaddresses of a digital image storage 12 from the present synchronizingsignals, the analog-to-digital-converted RGB signals being stored in itsstorage locations.

In FIG. 1, a dashed line is drawn through the center of the imagestorage 12 indicating that readout and read-in are effected separatelywith respect to the image storage 12.

For reading out of the image storage, the addresses are given by thesystem control circuit 10 in accordance with the second set ofparameters for display. The RGB signals which can be used for displayare present in analog form at the outputs of the image storage after theRGB signals digitally stored in the image storage 12 have been convertedback to analog signals.

The analog RGB signals are applied to the inputs of a control device 14which controls a light source 16 with respect to color and brightness.As a rule, the light source 16 will not have the same primaries as thetransmitted RGB signals so that a matrix switching circuit is providedin the control device 14 for transforming the RGB signals to the primarycolors R', G', B' of the light source 16. The required transformationmatrix can vary depending on the standard since the RGB signals can bedefined according to the primaries of 25 the FCC standard or EBUstandard, for example. Therefore, the system control circuit 10 canadjust the components in the matrix switching circuit determining thematrix coefficients via a control line 18.

Further, the control device 14 also contains amplifiers and circuits fornonlinear rectification adapted to the light source 16, so that anoptimum brightness quality and color quality can be achieved by thelight source 16.

The light source 16 in the embodiment example contains three lasers 20for red, green and blue. In the embodiment example, these lasers 20 areSKYLIGHT 400 series argon lasers and krypton lasers available from thefirm COHERENT, in which the wavelengths of the lasers are selected at647.1 nm for red, 514.5 nm for green and 458.0 nm for blue by means ofBP 458 and BP 514, 5 filters available from Schott, Mainz, Germany.Since the light intensities of lasers of this type cannot change quicklyenough, the lasers 20 are operated in continuous wave operation andtheir light intensity is controlled by modulators 22. The modulators 22in this case are DKDP crystals which determine the light intensities viachanges in polarity. The modulators are controlled directly by thesignals R', G', B' supplied by the control device 14.

The light bundles exiting from the modulators are combined to form acommon light bundle 26 via dichroic mirrors 24 and are reflected via adeflecting mirror 28 into an optical system 30 which is arrangeddownstream and which directs the light bundle 26 onto a picture screen32. In the embodiment example of FIG. 1, the viewer is situated in thedirection of the thin arrow. Thus, rear projection is used. However, thesame principles used in the embodiment example in FIG. 1 can also beused for front projection.

Provided in the optical system 30 is a lens system 34 by which the lightbundle 26 is projected onto the picture screen 32. The optical system 30further contains a raster scanning device 36 which deflects the lightbundle 26 onto the picture screen 32 in a framewise and linewise mannerin order to generate a video picture. According to the invention, theraster scanning device is so designed that the light bundle 26 can beprojected within a given picture field on optional points of the picturescreen 32. A polygon mirror 38 is provided for linewise deflection onthe picture screen 32 in the x direction shown in FIG. 1, while theframewise deflection is carried out in the y direction shown in thedrawing by means of a swiveling mirror 40.

The polygon mirror 38 and swiveling mirror 40 are controlled by signalsfrom a raster control 42.The raster control 42 establishes not only therate of revolutions and the deflection of the swiveling mirror, but alsothe amplitude of the swiveling mirror 40 in order to take into accountpicture aspect ratios such as 3 to 4 or 9 to 16 in different standardswithout having to blank image points. This economizes on laser output.

In order to adjust the amplitudes and frequencies for polygon mirrorsand swiveling mirrors, the raster control 42 receives, via control lines44, the corresponding signals which are outputted by the system controlcircuit 10 in accordance with the second set of parameters. In order todispense with costly regulating devices, the synchronizing pulses forthe image to be displayed are not generated separately and thenreadjusted in a suitable manner, but rather are obtained by the rastercontrol 42 from the positions of the polygon mirror and swiveling mirrordetected by the raster control 42. For example, this sensing can beeffected inductively via magnets at the polygon mirror 38 or swivelingmirror 40. However, an additional laser could also be directed onto oneof the polygon surfaces and recorded at a determined position of itsreflected light bundle by means of a light-sensitive detector in orderto detect the position of the polygon mirror and obtain therefrom asynchronizing signal for the start of the line.

The synchronizing signal for the line which is obtained in this way isguided from the raster control 42 to the system control circuit 10 inorder to control the image storage 12. In so doing, the operating timesof the image storage 12 are taken into account in that the synchronizingsignals are outputted at a specified time interval prior to the start ofthe line. However, memory delays of the image storage 12 can vary inlength depending on whether or not an algorithm is required forgenerating intermediate lines and depending on how time-consuming thisis. Therefore, the synchronizing signals are outputted prior to thestart of the line by a fixed time interval which is greater than thelongest possible memory delay in the image storage and the synchronizingsignals are then delayed via a delay circuit 46 whose delay time isadjusted by the system control circuit 10 for the delay actuallyrequired.

After passing through the delay circuit 46, the synchronizing signalsare fed to the system control circuit 10 where the addresses for thereadout of the image storage are generated, e.g., in that a counter iscounted up by the synchronizing signals.

In the example shown in FIG. 1, special requirements are imposed on theimage storage with respect to the time at which the color value signalsof image points are present at its outputs and, in particular, for thedata processing if a high-quality display is to be made possible up tothe high frequencies of 20 MHz required in the HDTV standard. Theconstruction of such image storages will be explained in more detailwith reference to the following figures.

FIG. 2 shows an image storage 12 in which the digitally converted colorvalue signals R_(i), G_(i), B_(i) are stored in a RAM (random-accessmemory) 48 and at whose outputs digitally stored color values R₀, G₀, B₀can be read out. The storage addresses are applied to the address lineof the RAM 48 from the storage readout addresses and the storageaddresses via a multiplexer 50, depending on whether readout or storageis to be effected. In FIG. 2, the multiplexer 50 and the storage in andreadout from a R/W (read/write) input of the RAM 48 are controlled by areadout pulse which is applied by the system control circuit 10 when thecolor vales R₀, G₀, B₀ are to be read out.

The simultaneous presence of readout and read-in addresses at the RAM 48is prevented in the circuit shown in FIG. 2 in that the color valuesignals for the display, R₀, G₀, B₀, are read out synchronously with thecontrolling of the image point by means of the swiveling mirror 40 andpolygon mirror 38. However, storage in the RAM 48 is not effecteddirectly. Rather, the color value signals to be stored and the storageaddresses are stored in a FIFO (first in, first out) storage 52 when soinitiated by a storage signal.

The storage signal is also present at a forward counting input of aforward-backward counter 54 which keeps track of the quantity of storeddata in the FIFO storage 52.

The contents of the FIFO storage 52 are only written into the RAM 48when no readout pulse is present. External clock signals serve totransfer the storage contents from the FIFO storage 52 to the RAM 48.These external clock signals are applied to a readout input of the FIFOstorage 52 via gates 55 and 56 only when there is no readout pulse forthe RAM 48 and the forward-backward counter 54 shows, via a NOR gate 58,that data are present in the FIFO storage. The forward-backward counter54 is reset via the clock during the readout of the FIFO storage.

Thus, the entered data for the color value signals R_(i), G_(i), B_(i)are entered asynchronously via a clock. For this purpose, the clockfrequency must be substantially higher than the clock rate for storingthe color values R, G, B in the video system. The higher the clock rate,the less storage space is required in the FIFO storage 52.

FIG. 3 shows a different solution to the problem of synchronization. Forthis purpose, the RAM 48 has two storage areas 1 and 2 or can be formedof two different storages with different addresses. The color valuesignals R_(i), G_(i), B_(i) are stored in RAM area 1 via a DMA module 60and transferred to RAM area 2 by means of a processor 62. The colorvalue signals can be read out of RAM area 2 again via a DMA module 64.In general, DMA modules such as those designated by 60 and 64 areadapted to an associated processor 62 in a data processing system so asto avoid the risk of synchronizing problems such as those described withreference to FIG. 2. However, in the case of time-critical response, itmay be necessary when reading out of the storage area 2 to put themicroprocessor in a holding state by means of the readout pulse asindicated by the readout arrow at the input HLT of processor 62.

In addition to the simplified synchronization with standard modules inFIG. 3, the processor 62 also provides the advantage that the data fordisplaying the image can be processed, for example, by applyingalgorithms to the data for determining intermediate lines or increasingresolution. For this purpose, data words are read in by the systemcontrol circuit 10 via a port 66 of the processor 62, which data wordsinstruct the processor 62 to carry out the selected algorithm for dataconversion and data transfer from RAM area 1 to RAM area 2.

Under time-critical transfer conditions, an individual processor 62 maybe too slow, so that a series of parallel processors 62 are used foraccessing different storage areas corresponding to various segments ofthe image.

Using the example of the read-out color value signal B₀, FIG. 3 furthershows how this color value signal can be further processed after beingread out of the RAM 48. The digital color value signal B₀ is firstconverted to an analog signal via a DAC 68 and is then guided via alow-pass filter 69. The low-pass filter 69 serves to suppress possiblehigh-frequency interference in the analog signal, e.g., originating fromthe intermediate frequency of a tuner. However, it also performs anotherfunction in that it smoothes the square analog values from the DAC 68and takes the mean of successive color values for image points over atime interval given by the low-pass filter 69. That is, given a suitabledesign of the low-pass filter 69, algorithms can be dispensed with bymeans of the processor 62 for adapting to a smaller quantity of imagepoints per line for display relative to the quantity of image points inthe stored video image. Therefore, an algorithm to be carried out by theprocessor 62 for averaging image points within a line can be dispensedwith, which accelerates the transfer of data from RAM area 1 to RAM area2. The low-pass filter 69 is then advisably adjustable to different timeconstants by the system control circuit 10, e.g., in that differentcapacitors are switched on in the low-pass filter 69 via analogswitches. However, a time shift in the signal maximum is also caused bythe low-pass filter 69 so that the time constant of the low-pass filter69 should be taken into account when adjusting the delay circuit 46 bymeans of the system control circuit 10.

In the event that it is desirable to take an average of a plurality ofimage points via the low-pass filter 69, the time constant of thelow-pass filter 69 is advisably selected so as to be proportional to thelowest number between the time per image point with respect to theparameter sets for storage and readout in the ROM 18, since theinformation content of an image can also not be increased by higherresolution on the one hand and, on the other hand, only the informationcontents given by the resolution of the second parameter set for displayis to be displayed. A selectable factor with respect to the cutofffrequency of the low-pass filter 69 also makes it possible to provide avarying degree of smoothing, which corresponds to differentinterpolations between image points within a line to be displayed.

As a result of the charging of capacitors in the low-pass filter 69, theblack-level porch can be shifted from one line to another in the videopicture. For this reason, a clamping circuit 70 is provided in thefollowing, which clamping circuit 70 pulls the output signal to zerobefore the line signal obtained in this way is sent to the controldevice 14 for further processing. Clamping by means of the clampingcircuit 70 is effected via the line synchronizing signal for the imageto be displayed.

For the purpose of reading the color value signals into and out of theRAM 48, the DMA modules 60 and 64 can be programmed by the controlcircuit 10, as is indicated by the wide arrows at modules 60 and 64.This can be carried out directly in some DMA modules, while in othersthe programming is effected via data lines leading to the processor. Inthe latter case, the values for programming must be read in via thecontrol circuit 10 by way of a port 66 of the microprocessor 62 whichthen transfers these values to the DMA modules 60, 64.

The time response shown in FIG. 3 is substantially determined by theprocessor times of the processor 62. At very high frequencies of up to20 MHz in HDTV, the example according to FIG. 3 can be realized by meansof processors which operate in parallel because of the excessiveslowness of currently available processors with respect to transfer forcomplex algorithms and high frequencies based on the second set ofparameters. However, this requires substantial investment.

FIG. 4 shows a simpler example in which a processor for data processingcan be dispensed with. The red color value signal Ro is used by way ofexample to illustrate the data processing shown in this figure, this redcolor value signal R₀ being read out of a RAM 48 designed according toFIG. 2. The same circuit can be used for the other color value signals.For the sake of a better understanding of the operation, it will beassumed in the following that a line n₀ is generated whose color valuesignal is given by weighted summation of the color value signals of twolines n_(i) and n_(i+1) of the image which is read into the imagestorage. Intermediate lines can also be generated by weighted summationif the number of lines of the image to be shown is greater than thenumber of lines of the image which is read into the image storage. Morethan two lines can also be summed with a circuit according to FIG. 4.However, for the sake of simplicity, the circuit is illustrated only fortwo lines n_(i) and n_(i+1).

After addressing via the system control circuit 10, two color values ofimage points, one for line n_(i) and one for line n_(i+1), are read outof the RAM 48 in each instance and stored in digital-to-analogconverters 72, 74 which are provided with input buffers. Thedigital-to-analog converters 72, 74 have a current output at which anoutput current is generated in proportion to the stored digital value.The output currents of the digital-to-analog converters 72 and 74 bringabout a voltage drop at adjustable resistors 76 and 78. Adjustableresistors can be realized, for instance, by connecting resistors viadigitally controllable analog switches, wherein the switching elementsmay be field-effect transistors.

The respective voltage drop at the adjustable resistors 76 and 78 issummed via an operational amplifier 80 which is designed with resistors81, 82, 83 in a manner which is known from the prior art. Thus, thereoccurs at the output of the operational amplifier 80 a voltage for thered color value signals of the line n₀ to be displayed, formed of colorvalues of the stored image points of lines n_(i) and n_(i+1) of theoperational amplifier 80, which color values are weighted in accordancewith the values of the adjustable resistors 76 and 78. In this way, theintermediate line n₀ is interpolated from lines n_(i) and n_(i+1). Forthis purpose, the digital values for weighting are read out of a ROM 85which is addressable with the digital value for the line n₀ to be readout. Thus, different weights can be adjusted via the ROM 85 for thedifferent framewise position of line n₀ in the image relative to theinput lines n_(i) and n_(i+) so that a circuit of this type can also beused in the case of non-integral multiples of the lines of the storedimage with respect to the read-out image. Further, the ROM 85 isaddressed by the system control circuit 10 with a data word, designatedas "Mode", so that different storage areas in the ROM can be addressed.Different types of interpolation can be determined by means of the dataword by selecting the utilized weights. The data word "Mode" is formeddepending on the ratio of output lines to be displayed to the number oflines in the stored image.

Further, the circuit in FIG. 4 again shows a low-pass filter 69 and aclamping circuit 70, so that an average may be taken over a plurality ofimage points in a line by means of the low-pass filter 69 withoutshifting the black level, as was already described in detail withreference to FIG. 3.

Thus, the processing of data in accordance with a circuit shown in FIG.4 permits interpolation of the color value signals of lines with respectto image points located one above the other with reference to the frameand following consecutively in time. However, in the case of morecomplex algorithms, image points lying on the diagonals of an image areusually also taken into consideration. Such algorithms can also berealized by a circuit according to FIG. 4 when color value signals ofimage points which are offset with respect to time are stored at theinput side in the additional digital-to-analog converter and are summedvia additional adjustable resistors and additional resistors at theinput of the operational amplifier 80. Thus, the added expenditure oncircuitry for taking into account more than two image points in thelinewise calculation with reference to FIG. 4 is minor so that complexalgorithms can also be realized by means of such a construction.

While the foregoing description and drawings represent the presentinvention, it will be obvious to those skilled in the art that variouschanges may be made therein without the departing from the true spiritand scope of the present invention.

We claim:
 1. In a video system for displaying a video picture composedof image points, whose color values and/or brightness values are storedsequentially, according to a first set of parameters with predeterminedparameter values containing number of lines, number of image points,line frequency and frame frequency as parameters, in an image storagewhich can be read out in accordance with a second set of parameters withdifferent or identical parameter values for the parameters fordisplaying the stored video picture by a display device, an improvementcomprising that:said display device contains an individual light sourcewhich is controlled in accordance with the color values and/orbrightness values of the image points and having an associated lightbundle; an optical system for projecting said light bundle onto apicture screen, said optical system having a raster scanning device bywhich said light bundle can be directed onto said picture screen onoptional points within an image field for displaying a video picture ofsuitable dimensions; and a raster control being provided for said rasterscanning device for rastering said light bundle in accordance with thesecond set of parameters; and wherein the image storage includes adigital storage for storing the color values and/or brightness values ofthe image points, and the digital storage includes a priority circuitwhich, in the event of simultaneous addressing for storing informationin storage locations and for reading information out of storagelocations, gives priority to the addressing for readout, temporarilystores the address for storage as well as the information to be stored,and only stores this information in the storage when the readout isconcluded.
 2. The video system according to claim 1, wherein the rasterscanning device has mirrors for deflecting the light bundle.
 3. Thevideo system according to claim 2, wherein the mirrors are constructedas at least one of rotating mirrors and swiveling mirrors.
 4. The videosystem according to claim 1, wherein the image storage can be acted uponby synchronizing pulses for at least one of the start of the line andthe start of the frame from the raster control for the readout of thevideo picture.
 5. The video system according to claim 4, wherein thesynchronizing pulses of the raster control are capable of beinggenerated prior in time to the start of each line which is given by theraster control by a time interval determined by the maximum memorydelays, and a delay circuit is provided for adapting the synchronizingsignals to the actual delay time.
 6. The video system according to claim1, wherein the quantity of available storage locations in the digitalstorage is greater than or equal to the number of required storagelocations for storing the color values and/or brightness valuesmultiplied by the maximum number of displayable image points, and theavailable storage locations for the color information and/or brightnessinformation are freely addressable.
 7. The video system according toclaim 6, wherein an image processing device, is provided whichinterpolates the image points, in accordance with the second parameterset for display, from the brightness values and/or color values of thestored video picture when the number of image points and/or the numberof lines in the first parameter set differs from that in the secondparameter set.
 8. The video system according to claim 7, wherein asecond storage area is provided in which brightness values and/or colorvalues which are interpolated by the image processing device are storedfor readout for the display device.
 9. The video system according toclaim 7, wherein more than one line is able to be read into the imageprocessing device from the image storage, wherein the color valuesand/or brightness values of the image points of the lines which are readin are adapted to being subjected to analog summation in a weightedmanner for generating a line for display.
 10. In a video system fordisplaying a video picture composed of image points, whose color valuesand/or brightness values are stored sequentially, according to a firstset of parameters with predetermined parameter values containing numberof lines, number of image points, line frequency and frame frequency asparameters, in an image storage which can be read out in accordance witha second set of parameters with different or identical parameter valuesfor the parameters for displaying the stored video picture by a displaydevice an. improvement comprising that:said display device contains anindividual light source which is controlled in accordance with the colorvalues and/or brightness values of the image points and having anassociated light bundle; an optical system for projecting said lightbundle onto a picture screen, said optical system having a rasterscanning device by which said light bundle can be directed onto saidpicture screen on optional points within an image field for displaying avideo picture of suitable dimensions; and a raster control beingprovided for said raster scanning device for rastering said light bundlein accordance with the second set of parameters; wherein an imageprocessing device is provided which interpolates the image points, inaccordance with the second parameter set for display, from thebrightness values and/or color values of the stored video picture whenthe number of image points and/or the number of lines in the firstparameter set differs from that in the second parameter set; and,wherein a low-pass filter is provided in the image processing device,said low-pass filter having a cutoff frequency which is given by apredetermined factor multiplied by the smallest product of imagepoint/line times the line frequency with respect to both sets ofparameters.
 11. The video system according to claim 10, wherein aclamping circuit is provided downstream of the low-pass filter.
 12. Thevideo system according to claim 10, wherein a circuit is provided forcolor adaptation for different signal definitions for color valuesand/or brightness values in the parameter sets for storage and readout.13. The video system according to claim 12, wherein said imageprocessing device is a video processor.